A paperboard printer slotter is exemplary of a machine which has a plurality of slotting heads mounted on a common shaft. Prior to a production run, it is frequently necessary to readjust the positions of the slotting heads and knives due to a change in the size of the paperboard blank to be processed.
The paperboard blank is generally provided with three pairs of slots as it passes through the slotting portion of the printer slotter. Three slots are cut into the leading edge of the paperboard blank and three slots are cut into the trailing edge of the paperboard blank. Each slot on the leading edge is aligned with a slot on the trailing edge. All of said slots are cut by the knives on a single shaft with one blank being processed per revolution of said shaft.
Conventional slotting heads on a printer slotter are provided with at least two slotter knives which project beyond the periphery of the head and each knife is adapted to cooperate with an annular groove in an opposing female slotting head. The slotting heads are mounted on rotatable parallel shafts. The slotter knives have been customarily attached to their respective heads by clamping bolts. The clamping bolts are adapted to be loosened manually so that the knives may be circumferentially adjusted on their heads in order that they may be used to slot different sizes of box blanks.
U.S. Pat. Nos. 2,117,220 and 3,003,403 are exemplary of the prior art. In order to adjust a slotter knife, it is necessary to move sections of the printer-slotter away from each other to facilitate access to the slotting heads. Thereafter, bolts are loosened and one knife is adjusted circumferentially with respect to the other head. After each knife has been adjusted, the sections of the printer slotter are then moved to a closed operative disposition. In the course of a day's operation, 10-20% of the time may be used in adjusting the elements of the printer slotter to process different sizes of paperboard box blanks.
An attempt was made in a prior art slotter to set the knives on all heads simultaneously. In this design, one knife is fixed to the slotter head in the normal fashion, with the second knife bolted to a ring gear in the head. A shaft through all heads engaging the ring gear has a single control mechanism on the center head so all knives can be positioned at one time.